1. Field of the Invention
The present invention relates to a belt sander having an endless abrasive belt trained over a pair of rollers. More particularly, the present invention relates to a device to prevent lateral drift of the abrasive belt for use in such a belt sander.
2. Description of the Prior Art
The abrasive belt of a typical sander is subject to lateral shifting during operation due to the undesirable inclination of one of the two rollers over which the belt is trained and also due to the manufacturing variations in the belt structure itself, such as the difference between the right and left circumferential lengths.
Various devices have been proposed to eliminate this problem: Japan Published Examined Utility Model Application No. H6-34927 discloses a device in which a yoke for mounting one of the belt rollers is pressed toward a frame via steel balls by compression springs and adjusting screws in order to secure the roller in a predetermined position. This prevents the undesirable inclination of the roller that causes its lateral drift. Meanwhile, Japan Published Examined Utility Model Application No. H6-27326 discloses an improved control nut threaded into the shaft of one of the belt rollers so that, by rotating the nut, the inclination of the roller can be adjusted according to the lateral drift of the belt. This improved nut is designed so as not to be loosened by the vibration of the belt sander, thus maintaining the correct inclination of the roller at which the abrasive belt does not drift laterally.
These devices, however, have poor operability in that they require manual adjustment by the operator: in the first device, the operator needs to remove the abrasive belt and rotate the screws for proper adjustment; in the latter, the control nut needs to be also rotated each time a new belt is installed.